Metered-dose inhalers (MDIs) are medication delivery devices that deliver a pharmaceutical formulation including one or more pharmaceutically active compounds (“active ingredients”) to a human or other mammalian patient.
Typically the pharmaceutical formulation is delivered by the MDI as unit doses in the form of an aerosol. Each actuation of the MDI delivers one unit dose. The unit dose is expelled by the MDI and is taken into the body of the patient on inhalation, via the nose or mouth. The pharmaceutical formulation is delivered to or via the respiratory tract, notably to the lungs, of the patient on inhalation.
The MDI includes a metering valve which is configured to ensure that each dose of the pharmaceutical formulation expelled by the MDI is the same, within permitted tolerances. In particular, each dose should include the same amount of the active ingredient(s). Generally, the metering valve is configured to dispense a constant volume of the pharmaceutical formulation on each actuation of the MDI.
Although efforts have been made to provide mechanical dose counters, these dose counters may add significant cost and materials to the device and may be inaccurate. Mechanical dose counters may not be able to differentiate events when a dose is actually delivered as compared with other events, such as when a metered-dose inhaler is dropped on the ground or otherwise experiences movement that does not press the metering valve sufficiently for a dose to be delivered. Hence mechanical dose counters have not gained widespread acceptance from healthcare providers. Electro-mechanical and electronic dose counters have also been proposed but have yet to achieve a sufficiently low cost and sufficiently high reliability.